For many of us, The Joy of Sex was our first (usually accidental) introduction to pubes. For its publishers, it was a challenge — how do you show people how to have sex without showing actual, well, sex? Very carefully, it turns out.

The BBC reports that Penguin, the book's publisher, wanted to avoid being charged with obscenity, and thus they knew that in order to accurately depict sex in an instructive way, they had to find a way to illustrate it.

Originally, the people behind the book planned to hire people from London's sex industry to perform the actions described in the book. Their photograph would be taken, and illustrators would work from those photos. However, the sex workers would often stop in the middle and ask for more money, so that plan had to be scrapped.

One of the book's illustrators ended up volunteering to model for the photographs that would later become the famous black and white illustrations. Over two days in 1972, Charles Raymond and his wife twisted and tangled their bodies into all sorts of positions and were photographed dozens of times.

As photography in sex books has become de rigueur, the age of the pencil drawing to avoid obscenity laws seems quaint and dated. But the legacy of The Joy of Sex lives on— both in its beautiful illustrations and in its unmovable place in many people's accidental sexual awakenings.